Central autonomic control mechanisms have been studied primarily in anesthetized animals; very little is known of central autonomic modulation in unanesthetized animals, and even less is known of these mechanisms in man. This proposal comprises three interrelated series of experiments, built around new, versatile, noninvasive research techniques, designed to explore central autonomic mechanisms. In the first, afferent autonomic input and central respiratory baroreflex gating will be manipulated experimentally to construct systematically, a unified theory of central vagal cardiac modulation in man. In the second series, dynamic fluctuations of central baroreflex gain will be sought in patients during spontaneous angina pectoris. In the third study, baroreflex responses will be analyzed with control systems methods to develop a mathematical model of the kinetics of cholinergic, baroreflex mediated sinus node inhibition. The goal of these studies is to develop a new organum of understanding about autonomic function in man which will transcend current perceptions in depth and breadth.